We have previously found that high dose oral amiodarone (1200-1600 mg/day for 10 days) improves cardiac symptoms, prolonges exercise capacity, and reduces significant ventricular arrhythmias in patients with nonbstructive hypertrophic cardiomyopathy and severe cardiac symptoms. The present investigation was designed to assess the chronic effects of amiodarone in the same patient group while on lower dose maintenance therapy (400-600 mg/day for 2 months). Efficacy was determined by exercise testing, ambulatory ECG monitoring, radionuclide cine-angiography, and semiquantitative symptoms score analysis. We found that exercise capacity improved significantly during chronic oral therapy in association with a reduction in the semiquantitative symptoms scores. The clinical responses were varied; one patient died suddenly despite improved symptoms and no ventricular arrhythmias, two others required the addition of calcium channel blockers, one had progressed to left ventricular myectomy, and 6 patients had satisfactory symptom control. It is our impression that amiodarone may prove to be significant tool in the pharmacologic armamentarium in the treatment of patients with hypertrophic cardiomyopathy. In addition to its important effects on both supraventricular and ventricular arrhythmias, amiodarone improves cardiac symptoms and restores functional capacity in many patients with hypertrophic cardiomyopathy who have been refractory to standard medical including calcium channel blockers and beta blockers.